A vehicle is known that includes an engine, a fluid power transmission device, and a clutch disposed between an input side member and an output side member of the fluid power transmission device. For example, this corresponds to a vehicle including a torque converter with a lockup clutch in a power transmission path between an engine and a transmission. In such a vehicle, a technique is known that provides slip control of putting the lockup clutch into slip-engagement (partial engagement) if a predetermined condition is satisfied. For example, this corresponds to a controller of a clutch described in Patent Document 1. It is described that this technique provides the slip control of a lockup clutch to set differential rotation between an input rotation member and an output rotation member of the torque converter to a target value, thereby enabling a responsive slip control with stability ensured even when the engine is in a high-rotation high-torque state.